1. Field of the Invention
This invention relates to electronic package units and more particularly to an improved method of assembling a hollow cavity plastic package using a simple and reliable sealing arrangement for shielding and protecting a semi-conductor element or semi-conductor integrated circuit element within the cavity, from the ambient atmosphere.
2. Description of the Prior Art
Common to prior art plastic sealing arrangements is the direct mold plastic package system for shielding electronic elements. In such arrangements, the electronic element and the internal lead wire which connects the internal portions of the external lead wires to the electronic element, are completely embedded in a plastic package wall such as epoxide resin polymer, which renders the electronic unit well-suited for mass production.
Such an arrangement, however, creates a number of problems including the inability to provide consistently reliable sealing arrangements particularly with respect to the external leads which protrude outwardly from the internal cavity housing the element as well as the breaking or severing of the internal lead wires caused by residual stresses in the plastic polymer or thermal stresses set up during the heat cycle.
Prior art sealing arrangements which have been employed in an attempt to eliminate the above problems, suggest that the internal lead wires should be completely free within the hollow package. In such sealing systems, which commonly are referred to as hermetically sealed electronic units, the electronic element is mounted within a hollow cavity of the package constructed of ceramic or metal and the ceramic or metal is then sealed by a low melting soldering glass.
The hermetic sealing arrangement does effectively prevent the breaking of the internal lead wires, however, it suffers the serious inherent problem of high cost.
The present invention is directed toward the provision of an improved method of assembling an electronic unit which provides reliable sealing, is well-suited for mass production at costs comparative to that of the direct mold unit, is easy to assemble, and assures consistently reliable operation without encountering any danger of breaking of the internal lead wires.
It has been found that the above objects of the present invention can be achieved by using a specific, improved sealing arrangement between the package and the external lead wires.